PARENT SESSION
Oral Session # 39: Limnology I: Ecosystems, Eutrophication, and Restoration.
Presiding: KL Cottingham
Wednesday, August 6. 8:00 AM to 11:30 AM, SITCC Meeting Room 101.
Structural changes in the pelagic food web of Lake Fryxell, Antarctica.
McKenna, Kerry*,1, Moorhead, Daryl1, Laybourn-Parry, Johanna2, Roberts, Emily2, 1 University of Toledo, Toledo, OH2 University of Nottingham, Nottingham, United Kingdom, United Kingdom
ABSTRACT- Total biomass of the pelagic food web of Lake Fryxell, Antarctica showed a significant increase from 1996 to 1998 (105 to 436 ug C/L, respectively). Mass also varied with depth, ranging from 161 ug C/L under surface ice, to a maximum 475 ug C/L at 9m, which corresponds to the deep chlorophyll maximum (DCM), then dropping to 275 ug C/L at 13m. Significant differences also existed among months with maximum values in December and January. Bacteria comprised the largest pool, and increased rapidly from <40 ug C/L at 8m to >300ug C/L at 10m. Stepwise linear regression showed that variation in bacterial biomass (R2=.61 p <0.001) was related to predator biomass and month. Photosynthetic nanoflagellates (PNAN) comprised the second largest pool, and showed greatest seasonal values in December, greatest annual values in 1998, and greatest values at 9m depth. Regression analysis revealed significant relationships (R2 =0.48 p < 0.001) to predators, month and year. Relative contributions of bacteria and PNAN changed with depth; bacteria increased below the chemocline whereas PNAN declined below this depth. Rotifer biomass decreased with depth and maximum values occurred in December and January. There was a significant relationship (p=0.0011) between rotifers, the top predator in this system and the biomass of the other plankton groups. Heterotrophic nanoflagellates (HNAN), herbaceous - and bacterial-feeding ciliates all increased significantly with depth (p=0.0001), with maximum values at the chemo-cline, with highest values in December and January. Variation in herbaceous- and bacterial-feeding ciliates were related to the biomass of their prey (p < 0.0001) and month.
Key words: antarctica, food-web, biomass